Increased default mode network connectivity associated with meditation

Areas associated with the default mode network (DMN) are substantially similar to those associated with meditation practice. However, no studies on DMN connectivity during resting states have been conducted on meditation practitioners. It was hypothesized that meditators would show heightened functional connectivity in areas of cortical midline activity. Thirty-five meditation practitioners and 33 healthy controls without meditation experience were included in this study. All subjects received 4.68-min resting state functional scanning runs. The posterior cingulate cortex and medial prefrontal cortex were chosen as seed regions for the DMN map. Meditation practitioners demonstrated greater functional connectivity within the DMN in the medial prefrontal cortex area (xyz=339-21) than did controls. These results suggest that the long-term practice of meditation may be associated with functional changes in regions related to internalized attention even when meditation is not being practiced.     

Temporal and instantaneous connectivity of default mode network estimated using Gaussian Bayesian network frameworks

By probing its functional anatomy, the default mode network (DMN) can be considered consisting of two interacting hub and non-hub subsystems. The hub subsystem includes posterior cingulate cortex (PCC), medial prefrontal cortex (MPFC) and bilateral inferior parietal cortex (IPC). The non-hub subsystem contains inferior temporal cortex (ITC) and (para) hippocampus (HC). In this study, Gaussian Bayesian Network (BN) and Gaussian Dynamic Bayesian Network (DBN) were applied separately to detect the instantaneous and temporal connection relationship within each and between the two DMN subsystems. It was found that the directional instantaneous interactions between the two subsystems were primarily “from non-hub to hub”. The temporal interactions between hub and non-hub regions, on the other hand, are less presented between the two subsystems. The hub subsystem demonstrated both strong instantaneous and temporal interactions among the hub regions, while the non-hub regions were only strongly inter-connected instantaneously but temporally isolated with each other. In addition, one of the hub regions, PCC, appears to be a confluent node and important in the functional integration within the network.     

Emotional faces and the default mode network

The default-mode network (DMN) of the human brain has become a central topic of cognitive neuroscience research. Although alterations in its resting state activity and in its recruitment during tasks have been reported for several mental and neurodegenerative disorders, its role in emotion processing has received relatively little attention. We investigated brain responses to different categories of emotional faces with functional magnetic resonance imaging (fMRI) and found deactivation in ventromedial prefrontal cortex (VMPFC), posterior cingulate gyrus (PC) and cuneus. This deactivation was modulated by emotional category and was less prominent for happy than for sad faces. These deactivated areas along the midline conformed to areas of the DMN. We also observed emotion-dependent deactivation of the left middle frontal gyrus, which is not a classical component of the DMN. Conversely, several areas in a fronto-parietal network commonly linked with attention were differentially activated by emotion categories. Functional connectivity patterns, as obtained by correlation of activation levels, also varied between emotions. VMPFC, PC or cuneus served as hubs between the DMN-type areas and the fronto-parietal network. These data support recent suggestions that the DMN is not a unitary system but differentiates according to task and even type of stimulus. The emotion-specific differential pattern of DMN deactivation may be explored further in patients with mood disorder, where the quest for biological markers of emotional biases is still ongoing.     

Age effect on the default mode network,inner thoughts,and cognitive abilities

Age-related effects on the default mode network (DMN) connectivity as measured at rest using functional magnetic resonance imaging (fMRI) are now well described. Little is known however about the relationships between these changes and age-related effects on cognition or on the unconstrained thoughts which occur during the resting-state scan, called inner experience. Brain resting-state activity, inner experience, and cognitive ability measurements were obtained in 70 participants aged 19–80 years. The anterior-posterior disruption of DMN activity with age reported in previous studies was recovered here. A significant effect of age was also found on cognitive abilities but not on inner experience. Finally, age-related changes in DMN connectivity were found to correlate with cognitive abilities, and more specifically with autobiographical memory performance. These findings provide new information to fuel the debate on the role of the brain default mode and more specifically on the effect of age-related changes in resting-state activity as measured with fMRI.     

基于动态功能连接分析的青少年吸烟者大脑静息态默认模式网络

采集30名青少年吸烟者和相匹配的30名非吸烟者的静息态功能性磁共振成像数据。通过独立成分分析、滑动窗相关法和k-均值聚类分析探讨青少年吸烟者的默认模式网络的动态功能连接变化。同时,使用斯皮尔曼相关分析评估动态功能连接指标（时间分数、平均停留时间和转换次数）与吸烟统计学数据（烟龄、包年和FTND）的关系。结果显示,相比于非吸烟组,青少年吸烟者大脑的默认模式网络的功能连接性降低,进一步的相关性分析表明动态功能连接指标中的平均停留时间与烟龄呈显著性正相关。此项研究从动态功能网络连接的角度分析吸烟对青少年吸烟者默认模式网络的影响,可以为进一步探索青少年吸烟成瘾机制提供新的视角。     

Functional connectivity in the pontomedullary respiratory network

Current models propose that a neuronal network in the ventrolateral medulla generates the basic respiratory rhythm and that this ventrolateral respiratory column (VRC) is profoundly influenced by the neurons of the pontine respiratory group (PRG). However, functional connectivity among PRG and VRC neurons is poorly understood. This study addressed four model-based hypotheses: 1) the respiratory modulation of PRG neuron populations reflects paucisynaptic actions of multiple VRC populations; 2) functional connections among PRG neurons shape and coordinate their respiratory-modulated activities; 3) the PRG acts on multiple VRC populations, contributing to phase-switching; and 4) neurons with no respiratory modulation located in close proximity to the VRC and PRG have widely distributed actions on respiratory-modulated cells. Two arrays of microelectrodes with individual depth adjustment were used to record sets of spike trains from a total of 145 PRG and 282 VRC neurons in 10 decerebrate, vagotomized, neuromuscularly blocked, ventilated cats. Data were evaluated for respiratory modulation with respect to efferent phrenic motoneuron activity and short-timescale correlations indicative of paucisynaptic functional connectivity using cross-correlation analysis and the "gravity" method. Correlogram features were found for 109 (3%) of the 3,218 pairs composed of a PRG and a VRC neuron, 126 (12%) of the 1,043 PRG–PRG pairs, and 319 (7%) of the 4,340 VRC–VRC neuron pairs evaluated. Correlation linkage maps generated for the data support our four motivating hypotheses and suggest network mechanisms for proposed modulatory functions of the PRG.     

Moral decision-making, ToM, empathy and the default mode network

Automatic intuitions and deliberate reasoning, sourcing internal representations of our personal norms and values, contribute to our beliefs of what is right and wrong. We used fMRI to directly compare moral (M) and non-moral (NM) decision-making processes using scenarios requiring conscious deliberation, whereby the main character declared an intention to take a course of action. Furthermore, we examined the relationship between BOLD signal, associated with M>NM decision-making, and moral judgment competence, psychopathy, and empathy. We observed greater activity in various parts of Theory of Mind, empathy and default mode networks during M>NM decision-making. There was a trend for high scores on primary psychopathy to correlate with decreased M>NM BOLD activation in an area extending from dorsolateral prefrontal cortex to medial prefrontal cortex. We suggest that moral decision-making entails a greater degree of internally directed processing, such as self-referential mental processing and the representation of intentions and feelings, than non-moral decision-making.     

Resting state fMRI in Alzheimer's disease: beyond the default mode network

Using resting state (RS) functional magnetic resonance imaging (fMRI), the connectivity patterns of the default mode (DMN), frontoparietal, executive, and salience networks were explored in 13 Alzheimer's disease (AD) patients, 12 amnestic mild cognitive impairment (aMCI) patients, and 13 healthy controls. Compared with controls and aMCI, AD was associated with opposing connectivity effects in the DMN (decreased) and frontal networks (enhanced). The only RS abnormality found in aMCI patients compared with controls was a precuneus connectivity reduction in the DMN. RS fMRI group differences were only partly related to gray matter atrophy. In AD patients, the mean executive network connectivity was positively associated with frontal-executive and language neuropsychological scores. These results suggest that AD is associated with an alteration of large-scale functional brain networks, which extends well beyond the DMN. In AD, the limited resources of the DMN may be paralleled, in an attempt to maintain cognitive efficiency, by an increased prefrontal connectivity. A medial parietal RS fMRI signal change seems to be present since the early phase of AD.     

Effects of mindfulness training on the default mode network in borderline personality disorder

Patients with borderline personality disorder (BPD) present dysfunctions of the default mode network (DMN). Mindfulness training has proven effective to improve the symptoms of BPD. The present study examines the effect of mindfulness training on BPD symptomatology and DMN activity during the performance of a working memory task in patients with BPD. Sixty‐five individuals with BPD were randomized to receive psychotherapy with either the mindfulness module of dialectical behavioural therapy (DBT‐M) or with interpersonal effectiveness module (DBT‐IE). The impact of treatments was evaluated with clinical and mindfulness variables as well as with functional magnetic resonance imaging during performance of the task. Both groups showed improvement in BPD symptoms and other clinical variables after treatment. Unexpectedly, there were no between‐group differences in DMN activation or deactivation. However, activation of the left anterior insula increased in both groups after the intervention. Compared with the control group, participants in the DBT‐M group presented higher deactivation in a cluster extending bilaterally from the calcarine to the cuneus and superior occipital gyri.     

Connectivity within the default mode network mediates the association between chronotype and sleep quality

A late chronotype is associated with poor sleep quality, but the fundamental neural mechanism underlying this association remains unclear. Eyes‐open resting‐state functional MRI scans were obtained from 87 participants after extended wakefulness, and four subregions of the default mode network were extracted and analysed. Partial correlation analysis revealed that the functional connectivity between the precuneus and the medial prefrontal cortex (mPFC) was significantly correlated both with sleep quality and circadian preference of the participants. Mediation analysis found that the precuneus–mPFC link fully mediated the correlation between chronotype and sleep quality. We concluded that increased neural communication in the midline cores of the default mode network (DMN) may be responsible for the poor sleep quality of late chronotypes. As late chronotypes exhibit vulnerability to many mental disorders, our results can be used to refine pathophysiological models and provide therapy for such psychological disorders.     

Fasting plasma insulin and the default mode network in women at risk for Alzheimer's disease

Brain imaging studies in Alzheimer's disease research have demonstrated structural and functional perturbations in the hippocampus and default mode network (DMN). Additional evidence suggests risk for pathological brain aging in association with insulin resistance (IR). This study piloted investigation of associations of IR with DMN-hippocampal functional connectivity among postmenopausal women at risk for Alzheimer's disease. Twenty middle-aged women underwent resting state functional magnetic resonance imaging. Subjects were dichotomized relative to fasting plasma insulin levels (i.e., > 8 μIU/mL [n = 10] and < 8 μIU/mL [n = 10]), and functional connectivity analysis contrasted their respective blood oxygen level-dependent signal correlation between DMN and hippocampal regions. Higher-insulin women had significantly reduced positive associations between the medial prefrontal cortex and bilateral parahippocampal regions extending to the right hippocampus, and conversely, between the left and right hippocampus and medial prefrontal cortex. Neuropsychological data (all within normal ranges) also showed significant differences with respect to executive functioning and global intelligence. The results provide further evidence of deleterious effects of IR on the hippocampus and cognition. Further imaging studies of the IR-related perturbations in DMN-hippocampal functional connectivity are needed.     

Age-related alterations in default mode network: impact on working memory performance

The default mode network (DMN) is a set of functionally connected brain regions which shows deactivation (task-induced deactivation, TID) during a cognitive task. Evidence shows an age-related decline in task-load-related modulation of the activity within the DMN during cognitive tasks. However, the effect of age on the functional coupling within the DMN and their relation to cognitive performance has hitherto been unexplored. Using functional magnetic resonance imaging, we investigated functional connectivity within the DMN in older and younger subjects during a working memory task with increasing task load. Older adults showed decreased connectivity and ability to suppress low frequency oscillations of the DMN. Additionally, the strength of the functional coupling of posterior cingulate (pCC) with medial prefrontal cortex (PFC) correlated positively with performance and was lower in older adults. pCC was also negatively coupled with task-related regions, namely the dorsolateral PFC and cingulate regions. Our results show that in addition to changes in canonical task-related brain regions, normal aging is also associated with alterations in the activity and connectivity of brain regions within the DMN. These changes may be a reflection of a deficit in cognitive control associated with advancing age that results in deficient resource allocation to the task at hand.     

默认模式网络在精神疾病诊断中的研究进展

脑影像技术的发展为探究精神类疾病的发病成因及治疗方案提供了更多途径。默认模式网络（DMN）是大脑静息状态下的主要工作模式。本研究综述近期精神疾病的DMN研究进展,明确了DMN的结构,总结主流的磁共振数据预处理工具箱以及与DMN相关的功能连接计算方法,进而分析利用DMN功能连接研究各类精神疾病的结果。最后提出现有研究中的结果与不足,并展望未来可能的研究方向。     

抑郁症静息态下注意网络功能连接的病例对照研究

目的:利用功能性核磁共振成像(fMRI)技术,观察静息态下抑郁症注意网络的功能连接。方法:26例符合中国精神障碍分类与诊断标准(第三版)(CCMD-3)单相抑郁症诊断标准,同时符合美国《精神障碍诊断与统计学手册》第四版(DSM-IV)重性抑郁诊断标准抑郁症住院患者及25名年龄、受教育年限匹配的健康对照者参与了静息态fMRI扫描。分别分析抑郁症患者前、后注意网络内区域相互之间低频fMRI信号波动的相关性,以观察抑郁症注意网络的功能连接。结果:与对照组相比,抑郁组双侧前扣带回与丘脑[左侧Z分:(0.58±0.10)vs.(0.64±0.06),P=0.012;右侧Z分:(0.53±0.13)vs.(0.61±0.13),P=0.025]、双侧基底神经节与丘脑[左侧Z分:(0.66±0.07)vs.(0.70±0.05),P=0.043,右侧Z分:(0.64±0.07)vs.(0.71±0.07),P=0.002]、左侧额叶皮层与前扣带回[Z分:(0.51±0.16)vs.(0.63±0.12),P=0.003]、左侧额叶皮层与基底神经节[Z分:(0.59±0.07)vs.(0.65±0.11),P=0.029]、右侧辅助运动区与基底神经节[Z分:(0.57±0.11)vs.(0.64±0.11),P=0.024]、右侧前扣带回与辅助运动区[Z分:(0.54±0.10)vs.(0.61±0.11),P=0.043]、右侧额叶皮层与辅助运动区的功能连接减低[Z分:(0.64±0.10)vs.(0.70±0.10),P=0.028]。结论:静息态抑郁症患者注意网络的功能连接存在异常,可能与抑郁症患者认知功能损害,尤其是注意力下降有关。     

Functional connectivity and laterality of the motor and sensory components in the volitional swallowing network

Functional neuroimaging has shown that multiple brain regions are active during volitional swallowing. Little is known, however, about which regions integrate motor execution and sensory feedback in the swallowing system. Although unilateral brain lesions in either hemisphere can produce swallowing deficits, some functional neuroimaging studies indicate that the left hemisphere has greater activation in certain sensory and motor-related swallowing regions. In this study, correlation coefficients were computed for five seed regions during volitional saliva swallowing to determine the functional relationships of these regions with the rest of the brain: the anterior and posterior insula, inferior frontal gyrus (BA44), primary sensory cortex (S1), and primary motor cortex (M1). A laterality index (LI) was derived that accounts for relative differences in total, positive connected voxels for the left/right hemisphere seeds. Clusters of significantly connected voxels were greater from the anterior and posterior insula than from the other three seed regions. Interactions of the insula with other brain regions were greater on the left than on the right during volitional swallowing. Group means showed laterality in the anterior insula (LI = 0.25) and the posterior insula (LI = 0.33). BA44 showed a lesser degree of difference in left versus right hemisphere interactions (LI = 0.12) while S1 did not show lateralization (LI = 0.02) and M1 showed some predominance of interactions in the right hemisphere (LI = −0.19). The greater connectivity from the left hemisphere insula to brain regions within and across hemispheres suggests that the insula is a primary integrative region for volitional swallowing in humans.     

Frontal theta EEG activity correlates negatively with the default mode network in resting state.

We used simultaneously recorded EEG and fMRI to investigate in which areas the BOLD signal correlates with frontal theta power changes, while subjects were quietly lying resting in the scanner with their eyes open. To obtain a reliable estimate of frontal theta power we applied ICA on band-pass filtered (2-9 Hz) EEG data. For each subject we selected the component that best matched the mid-frontal scalp topography associated with the frontal theta rhythm. We applied a time-frequency analysis on this component and used the time course of the frequency bin with the highest overall power to form a regressor that modeled spontaneous fluctuations in frontal theta power. No significant positive BOLD correlations with this regressor were observed. Extensive negative correlations were observed in the areas that together form the default mode network. We conclude that frontal theta activity can be seen as an EEG index of default mode network activity.     

Partial correlation investigation on the default mode network involved in acupuncture: An fMRI study

Certain clinical reports and researches have shown that acupuncture effects can sustain a period during the post-stimulation state, and modulate the default mode network (DMN). In this study, partial correlation approach was utilized to investigate whether or not electro-acupuncture stimulation (EAS) at the three acupoints (GB37 (Guangming), BL60 (Kunlun) and KI8 (Jiaoxin)) and one sham point on the left leg modulated the DMN and how to change the intrinsic connectivity of the DMN. The results indicated that DMN could be modulated after EAS, and there existed different modulation patterns of the four points. Meanwhile, we found that the posterior cingulate cortex and precuneus (PCC/pC) strongly interacted with other nodes during the pre- and post-stimulation states. The correlation was interrupted between the PCC/pC and anterior cingulate cortex (ACC). The orbital prefrontal cortex (OFC) negatively interacted with the left medial temporal cortex (lMTC) at the acupoints. We suggested that the distinct modulation patterns to the DMN attributed to the different effects evoked by the three acupoints and one sham point.     

Complexity of spontaneous BOLD activity in default mode network is correlated with cognitive function in normal male elderly: a multiscale entropy analysis

The nonlinear properties of spontaneous fluctuations in blood oxygen level-dependent (BOLD) signals remain unexplored. We test the hypothesis that complexity of BOLD activity is reduced with aging and is correlated with cognitive performance in the elderly. A total of 99 normal older and 56 younger male subjects were included. Cognitive function was assessed using Cognitive Abilities Screening Instrument and Wechsler Digit Span Task. We employed a complexity measure, multiscale entropy (MSE) analysis, and investigated appropriate parameters for MSE calculation from relatively short BOLD signals. We then compared the complexity of BOLD signals between the younger and older groups, and examined the correlation between cognitive test scores and complexity of BOLD signals in various brain regions. Compared with the younger group, older subjects had the most significant reductions in MSE of BOLD signals in posterior cingulate gyrus and hippocampal cortex. For older subjects, MSE of BOLD signals from default mode network areas, including hippocampal cortex, cingulate cortex, superior and middle frontal gyrus, and middle temporal gyrus, were found to be positively correlated with major cognitive functions, such as attention, orientation, short-term memory, mental manipulation, and language. MSE from subcortical regions, such as amygdala and putamen, were found to be positively correlated with abstract thinking and list-generating fluency, respectively. Our findings confirmed the hypothesis that complexity of BOLD activity was correlated with aging and cognitive performance based on MSE analysis, and may provide insights on how dynamics of spontaneous brain activity relates to aging and cognitive function in specific brain regions.     

Personality--life event congruence effects in late-life depression

BACKGROUND: This study examined whether specific interactions of personality and life events predicted increases in depressive symptoms over time in a late-life sample. METHOD: Participants (n=55) who were in remission from a recent episode of major depression completed a depression symptom interview and a questionnaire assessing the personality constructs sociotropy and autonomy. Six months later, they completed the same personality questionnaire and a checklist of life events experienced during the past 6 months. RESULTS: As predicted, increases in depressive symptoms were significantly predicted by the congruent interaction of sociotropy with negative interpersonal events and by the congruent interaction of autonomy with negative autonomy events, but not by either of the non-congruent interactions. LIMITATIONS: A small sample prevented examinations of important depressive subtypes based on age of depression onset and vascular status. CONCLUSIONS: These findings strongly support the personality-life event congruence model of depression in a late-life sample. Clinical implications include attending to stressful events that match an older adult's personality style, to help the older adult cope with those events that are more likely to increase his or her depression.